Field of the Art
This disclosure relates to the field of image processing, and is particularly concerned with the automatic construction of high-quality high-resolution orthomosaics from satellite or aerial imagery.
Discussion of the State of the Art
To build an orthomosaic from satellite or aerial imagery, participating images are first orthorectified, co-registered, and tonally balanced, and then a seamline vector is constructed for every pair (in essence) of images A and B that overlap. Once all these seamlines are computed, images are clipped by their seamlines to form mosaic regions that fit together like puzzle pieces. In high-quality orthomosaics, the seamlines are as inconspicuous as possible so that the mosaic actually appears seamless (seamlines are inconspicuous when local mosaic content shows natural transition going from one side of the seamline to the other.) In the past, to get this level of quality required manual construction of the seamlines—a tedious and labor-intensive process. Automated systems for constructing orthomosaics must generate seamlines automatically and, if required, necessitate only minimal human touch-up. An existing approach for doing this is to auto-generate a “cost” raster per seamline, and automatically extract the seamline as a least cost path between two points using, say, Dijkstra's algorithm. What has been missing is a recipe for creating a cost raster that leads to an inconspicuous seamline (inconspicuous over a diverse range of image content) and especially in the most complex areas where there is human development. Prior art cost rasters for seamline construction were based primarily on tonal similarity between corresponding pixels in the involved images—this is insufficient in many cases to yield an inconspicuous seamline.
What is needed is a way of constructing a cost raster that will lead to an inconspicuous seamline, over a diverse range of image content, especially in the most complex areas where there is human development. This is especially needed for high-quality, high-resolution, RGB orthomosaics that may be formed from any part of the globe.